Juvenile Male Rats Research Articles

Metabolic and histopathological impact of local resource food consumption on blood markers in rats previously subjected to moderate acute malnutrition

Malnutrition is caused by dietary and nutritional imbalances that can have an impact on blood parameters and vital organs. The use of local agricultural resources for adapted diets appears to be an effective solution to post-weaning infant malnutrition. The aim of this study was to evaluate the effectiveness of four newborn diets made from local agricultural resources in improving biochemical, hematological, and histological parameters in rats that had previously experienced mild acute malnutrition. A total of 42 juvenile male rats, with an average age of 80 ±5 days and an average weight of 103.46 ± 5.10 g, were divided into six groups. Each group consisted of seven rats, with two control groups (LTC and LSA) and four experimental groups (LAR1A, LAR1B, LAR2A, and LAR2B). The experiment had three distinct phases: an initial adaptation period lasting 5 days, followed by a phase of inducing malnutrition lasting 19 days, and finally a phase of nutritional rehabilitation lasting 14 days. At the conclusion of the malnutrition induction and nutritional rehabilitation phases, blood samples were collected and used to evaluate biochemical and haematological markers. Kidneys and liver were removed for histological analysis.The findings revealed that the period of inducing malnutrition had a detrimental impact on several parameters, such as urea, triglyceride, total protein, C-reactive protein, albumin, ALAT, ASAT, WBC, hemoglobin, hematocrit, and MCV. Nevertheless, the ingestion of LAR diet derived from indigenous ingredients successfully returned all of these blood markers to the required levels for rats. Furthermore, histological examinations demonstrated that there were no kidney or liver abnormalities at the end of the trial.The LAR diets have rehabilitative effects on the biochemical and haematological parameters of rats. This suggests that these diets can be used therapeutically to treat moderate acute malnutrition and meet the nutritional needs of children aged 6 to 36 months.

Ghrelin alleviated TiO2 NPs-induced inhibition of endochondral osteogenesis and promoted longitudinal growth of long bones in juvenile rats via Wnt/β-catenin signaling pathway

Titanium dioxide nanoparticles (TiO2 NPs) are widely used in children’s daily necessities and foods, and their health hazards to children have attracted particular attention. Childhood is a critical time for accelerated bone growth and development. Current studies revealed that TiO2 NPs exposure causes bone damage in juvenile rats; however, the underlying mechanism is unknown. Ghrelin is a polypeptide hormone that is considered to be a candidate factor for regulating bone growth and development. In this research, 3-week-old juvenile male rats were administered 0, 100 or 200 mg/kg TiO2 NPs and 50 μg/kg ghrelin for 4 weeks to explore the underlying mechanism of TiO2 NPs-induced bone damage, and the protective effect of ghrelin. Our results revealed that TiO2 NPs resulted in decreased synthesis of bone growth-related hormones, disturbed bone metabolism, and destruction of bone structure. Further mechanism studies showed that TiO2 NPs inhibited Wnt/β-catenin pathway, reduced collagen synthesis, inhibited chondrocyte proliferation and differentiation, promoted chondrocyte apoptosis, and inhibited endochondral osteogenesis, ultimately leading to long bone longitudinal growth retardation and osteoporosis. Ghrelin alleviated the negative effects of TiO2 NPs-induced bone growth in juvenile rats by upregulating the Wnt/β-catenin signaling pathway. This study provided a reference for the clinical treatment of growth retardation and idiopathic short stature in juvenile children caused by environmental pollutants.

Vasopressin regulates social play behavior in sex-specific ways through glutamate modulation in the lateral septum.

Understanding the neural basis of social play in juvenile rats may ultimately help restore social play deficits in autistic children. We previously found that administration of a vasopressin (AVP) V1a receptor (V1aR) antagonist into the lateral septum (LS) increased social play behavior in male juvenile rats and decreased it in females. Here, we demonstrate that glutamate, but not GABA, is involved in this sex-specific regulation. First, we found a sex difference in extracellular LS glutamate/GABA ratio (lower in females) that was eliminated by V1aR antagonist infusion in the LS that caused an increase in glutamate release in females only. Second, infusion of the glutamate receptor agonist L-glutamic acid into the LS mimicked the V1aR antagonist-induced decrease in female social play while preventing the increase in male social play. Third, infusion of the glutamate receptor antagonists AP-5 and CNQX into the LS prevented the V1aR antagonist-induced decrease in female social play. Fourth, there were no sex differences in extracellular GABA release in the LS upon either V1aR antagonist infusion or in social play expression upon infusion of the GABA-A receptor agonist muscimol into the LS, suggesting that GABA is not involved in the sex-specific regulation of social play by the LS-AVP system. Last, we found no sex differences in the type (GAD1/2, somatostatin, calbindin 1, Sox9) of V1aR-expressing LS cells, suggesting other cellular mechanisms mediating the sex-specific effects on glutamate release in the LS by the LS-AVP system. In conclusion, we demonstrate that the LS-AVP system regulates social play sex-specifically via glutamatergic neurotransmission. These findings have relevance for potential sex-specific effects of AVP-based treatment of social deficits in children.

Differential role of NMDA receptors in hippocampal-dependent spatial memory and plasticity in juvenile male and female rats.

Early life, or juvenility, stands out as the most pivotal phase in neurodevelopment due to its profound impact over the long-term cognition. During this period, significant changes are made in the brain's connections both within and between different areas, particularly in tandem with the development of more intricate behaviors. The hippocampus is among the brain regions that undergo significant postnatal remodeling, including dendritic arborization, synaptogenesis, the formation of complex spines and neuron proliferation. Given the crucial role of the hippocampus in spatial memory processing, it has been observed that spatial memory abilities continue to develop as the hippocampus matures, particularly before puberty. The N-methyl-d-aspartate (NMDA) type of glutamate receptor channel is crucial for the induction of activity-dependent synaptic plasticity and spatial memory formation in both rodents and humans. Although extensive evidence shows the role of NMDA receptors (NMDAr) in spatial memory and synaptic plasticity, the studies addressing the role of NMDAr in spatial memory of juveniles are sparse and mostly limited to adult males. In the present study, we, therefore, aimed to investigate the effects of systemic NMDAr blockade by the MK-801 on spatial memory (novel object location memory, OLM) and hippocampal plasticity in the form of long-term potentiation (LTP) of both male and female juvenile rats. Our results show the sex-dimorphic role of NMDAr in spatial memory and plasticity during juvenility, as systemic NMDAr blockade impairs the OLM and LTP in juvenile males without an effect on juvenile females. Taken together, our results demonstrate that spatial memory and hippocampal plasticity are NMDAr-dependent in juvenile males and NMDAr-independent in juvenile females. These sex-specific differences in the mechanisms of spatial memory and plasticity may imply gender-specific treatment for spatial memory disorders even in children.

High-fat diet consumption negatively influences closed-head traumatic brain injury in a pediatric rodent model

Traumatic brain injury (TBI) is one of the most common causes of emergency room visits in children, and it is a leading cause of death in juveniles in the United States. Similarly, a high proportion of this population consumes diets that are high in saturated fats, and millions of children are overweight or obese. The goal of the present study was to assess the relationship between diet and TBI on cognitive and cerebrovascular outcomes in juvenile rats. In the current study, groups of juvenile male Long Evans rats were subjected to either mild TBI via the Closed-Head Injury Model of Engineered Rotational Acceleration (CHIMERA) or underwent sham procedures. The animals were provided with either a combination of high-fat diet and a mixture of high-fructose corn syrup (HFD/HFCS) or a standard chow diet (CH) for 9 days prior to injury. Prior to injury, the animals were trained on the Morris water maze for three consecutive days, and they underwent a post-injury trial on the day of the injury. Immediately after TBI, the animals' righting reflexes were tested. Four days post-injury, the animals were euthanized, and brain samples and blood plasma were collected for qRT-PCR, immunohistochemistry, and triglyceride assays. Additional subsets of animals were used to investigate cerebrovascular perfusion using Laser Speckle and perform immunohistochemistry for endothelial cell marker RECA. Following TBI, the righting reflex was significantly increased in TBI rats, irrespective of diet. The TBI worsened the rats' performance in the post-injury trial of the water maze at 3 h, p(injury) < 0.05, but not at 4 days post-injury. Reduced cerebrovascular blood flow using Laser Speckle was demonstrated in the cerebellum, p(injury) < 0.05, but not foci of the cerebral cortices or superior sagittal sinus. Immunoreactive staining for RECA in the cortex and corpus callosum was significantly reduced in HFD/HFCS TBI rats, p < 0.05. qRT-PCR showed significant increases in APOE, CREB1, FCGR2B, IL1B, and IL6, particularly in the hippocampus. The results from this study offer robust evidence that HFD/HFCS negatively influences TBI outcomes with respect to cognition and cerebrovascular perfusion of relevant brain regions in the juvenile rat.

Play partner preferences among groups of unfamiliar juvenile male rats

Like many mammals, as juveniles, rats engage in play fighting, which in the laboratory is typically studied in dyads, and consequently, it is the researcher who determines a rat’s play partner. In real-life conditions, a rat would have many partners with whom to play. In a previous study, we found that rats do prefer to play with some individuals more than others, and surprisingly, when given the choice, unfamiliar partners are preferred to familiar ones. In this study, we assessed partner choice when all the available partners are strangers. Eight groups of six unfamiliar juvenile male rats were observed for 10 min play trials. One of the six in each group was selected as the ‘focal’ rat and his play towards, and received by, the others were scored. Social networks revealed that five of the eight groups formed preferences, with preferred partners also engaging in more play with the focal rat. The mechanism by which these preferences were formed remains to be determined, but it seems that there are individual differences, potentially in the amount and style of play, that allow an individual to select the most suitable partner from a group of strangers.

Early-life bisphenol A exposure causes neuronal pyroptosis in juvenile and adult male rats through the NF-κB/IL-1β/NLRP3/caspase-1 signaling pathway: exploration of age and dose as effective covariates using an in vivo and in silico modeling approach

Early-life bisphenol A exposure causes neuronal pyroptosis in juvenile and adult male rats through the NF-κB/IL-1β/NLRP3/caspase-1 signaling pathway: exploration of age and dose as effective covariates using an in vivo and in silico modeling approach

Sex differences in the structure and function of the vasopressin system in the ventral pallidum are associated with the sex-specific regulation of social play behavior in juvenile rats

Vasopressin (AVP) regulates various social behaviors, often in sex-specific ways, including social play behavior, a rewarding behavior displayed primarily by juveniles. Here, we examined whether and how AVP acting in the brain's reward system regulates social play behavior in juvenile rats. Specifically, we focused on AVP signaling in the ventral pallidum (VP), a brain region that is a part of the reward system. First, we examined the organization of the VP-AVP system in juvenile rats and found sex differences, with higher density of both AVP-immunoreactive fibers and AVP V1a receptor (V1aR) binding in males compared to females while females show a greater number of V1aR-expressing cells compared to males. We further found that, in both sexes, V1aR-expressing cells co-express a GABA marker to a much greater extent (approx. 10 times) than a marker for glutamate. Next, we examined the functional involvement of V1aR-expressing VP cells in social play behavior. We found that exposure to social play enhanced the proportion of activated V1aR-expressing VP cells in males only. Finally, we showed that infusion of a specific V1aR antagonist into the VP increased social play behaviors in juvenile male rats while decreasing these behaviors in juvenile female rats. Overall, these findings reveal structural and functional sex differences in the AVP-V1aR system in the VP that are associated with the sex-specific regulation of social play behavior.

Granulocyte- Macrophage Colony-Stimulating Factor Reverses Immunosuppression Acutely Following a Traumatic Brain Injury and Hemorrhage Polytrauma in a Juvenile Male Rat Model.

Traumatic brain injury (TBI) is a common cause of morbidity and mortality in children. We have previously shown that TBI with a concurrent extracranial injury reliably leads to post-injury suppression of the innate and adaptive immune systems. In patients with post-injury immune suppression, if immune function could be preserved, this might represent a therapeutic opportunity. As such, we examined, in an animal injury model, whether systemic administration of granulocyte macrophage colony-stimulating factor (GM-CSF) could reverse post-injury immune suppression and whether treatment was associated with neuroinflammation or functional deficit. Prepubescent male rats were injured using a controlled cortical impact model and then subjected to removal of 25% blood volume (TBI/H). Sham animals underwent surgery without injury induction, and the treatment groups were sham and injured animals treated with either saline vehicle or 50 μg/kg GM-CSF. GM-CSF was administered following injury and then daily until sacrifice at post-injury day (PID) 7. Immune function was measured by assessing tumor necrosis factor-α (TNF-α) levels in whole blood and spleen following ex vivo stimulation with pokeweed mitogen (PWM). Brain samples were assessed by multiplex enzyme-linked immunosorbent assay (ELISA) for cytokine levels and by immunohistochemistry for microglia and astrocyte proliferation. Neuronal cell count was examined using cresyl violet staining. Motor coordination was evaluated using the Rotarod performance test. Treatment with GM-CSF was associated with a significantly increased response to PWM in both whole blood and spleen. GM-CSF in injured animals did not lead to increases in levels of pro-inflammatory cytokines in brain samples but was associated with significant increases in counted astrocytes. Finally, while injured animals treated with saline showed a significant impairment on behavioral testing, injured animals treated with GM-CSF performed similarly to uninjured animals. GM-CSF treatment in animals with combined injury led to increased systemic immune cell response in whole blood and spleen in the acute phase following injury. Improved immune response was not associated with elevated pro-inflammatory cytokine levels in the brain or functional impairment.

Peripherally-derived LGI1-reactive monoclonal antibodies cause epileptic seizures in vivo.

One striking clinical hallmark in patients with autoantibodies to leucine-rich glioma inactivated 1 (LGI1) is the very frequent focal seizure semiologies, including faciobrachial dystonic seizures (FBDS), in addition to the amnesia. Polyclonal serum IgGs have successfully modelled the cognitive changes in vivo but not seizures. Hence, it remains unclear whether LGI1-autoantibodies are sufficient to cause seizures. We tested this with the molecularly precise monoclonal antibodies directed against LGI1 [LGI1-monoclonal antibodies (mAbs)], derived from patient circulating B cells. These were directed towards both major domains of LGI1, leucine-rich repeat and epitempin repeat, and infused intracerebroventricularly over 7 days into juvenile male Wistar rats using osmotic pumps. Continuous wireless EEG was recorded from a depth electrode placed in hippocampal CA3 plus behavioural tests for memory and hyperexcitability were performed. Following infusion completion (Day 9), post-mortem brain slices were studied for antibody binding and effects on Kv1.1. The LGI1-mAbs bound most strongly in the hippocampal CA3 region and induced a significant reduction in Kv1.1 cluster number in this subfield. By comparison to control-Ab injected rats video-EEG analysis over 9 days revealed convulsive and non-convulsive seizure activity in rats infused with LGI1-mAbs, with a significant number of ictal events. Memory was not impaired in the novel object recognition test. Peripherally-derived human LGI1-mAbs infused into rodent CSF provide strong evidence of direct in vivo epileptogenesis with molecular correlations. These findings fulfill criteria for LGI1-antibodies in seizure causation.

Gross morpho-biometry, histometry and immunohistochemical investigations of pituitary gland in the juvenile and adult male African giant rats (Cricetomys gambianus)

This work was designed to investigate the morphometry and immunohistochemical features of pituitary glands in the African Giant Rats (AGR). Adult and juvenile AGR were sacrificed and their brains harvested, and the pituitary glands were carefully dissected. The weight, length and width of brains and pituitary glands were subsequently measured. Sections were prepared and stained using Haematoxylin and Eosin (H&amp;E), Cresyl-violet and periodic-acid-Schiff (PAS) for histological analysis. Immunohistochemical analysis was carried out with Glial-Fibrillary-Acidic-Protein (GFAP) and Ionized-Calcium-Binding-Adapter-Molecule 1 (Iba1). Grossly, the AGR pituitary gland is a somehow laterally extended, saddle-shaped organ that is dorso-ventrally flattened. The gray-coloured adenohypophysis (anterior-pituitary lobe) was bigger in size than the whitish neurohypophysis (posterior-pituitary lobe) on physical examination. Histometrically, the adenohypophyseal length was noticeably greater than that of neurohypophysis in both juvenile and adult. Similarly, the adenohypophyseal and neurohypophyseal width in adult were found to be more than that of juvenile. Also, the histological staining of the neurohypophysis and adenohypophysis were distinct. In the neurohypophysis, fibrous and protoplasmic pituicytes were observed among fibres and Herring-bodies. Chromophils and chromophobes were identified in the adenohypophysis and melanotrophs in the intermediate lobe. Immunohistochemistry showed pituicytes in the neurohypophysis, which was positive with GFAP-antibody. With Iba1-antibody, the neurohypophysis expressed a stronger positive immunolabelling to microglia as compared to macrophages in the adenohypophysis. In conclusion, the gross and microscopic characteristics of pituitary glands of the AGR are found to be similar to other rodents and mammals. We recommend further study to compare morphometrical parameters between male and females of this model.

Hearing loss in juvenile rats leads to excessive play fighting and hyperactivity, mild cognitive deficits and altered neuronal activity in the prefrontal cortex

BackgroundIn children, hearing loss has been associated with hyperactivity, disturbed social interaction, and risk of cognitive disturbances. Mechanistic explanations of these relations sometimes involve language. To investigate the effect of hearing loss on behavioral deficits in the absence of language, we tested the impact of hearing loss in juvenile rats on motor, social, and cognitive behavior and on physiology of prefrontal cortex. MethodsHearing loss was induced in juvenile (postnatal day 14) male Sprague-Dawley rats by intracochlear injection of neomycin under general anesthesia. Sham-operated and non-operated hearing rats served as controls. One week after surgery auditory brainstem response (ABR) measurements verified hearing loss or intact hearing in sham-operated and non-operated controls. All rats were then tested for locomotor activity (open field), coordination (Rotarod), and for social interaction during development in weeks 1, 2, 4, 8, 16, and 24 after surgery. From week 8 on, rats were trained and tested for spatial learning and memory (4-arm baited 8-arm radial maze test). In a final setting, neuronal activity was recorded in the medial prefrontal cortex (mPFC). ResultsIn the open field deafened rats moved faster and covered more distance than sham-operated and non-operated controls from week 8 on (both p < 0.05). Deafened rats showed significantly more play fighting during development (p < 0.05), whereas other aspects of social interaction, such as following, were not affected. Learning of the radial maze test was not impaired in deafened rats (p > 0.05), but rats used less next-arm entries than other groups indicating impaired concept learning (p < 0.05). In the mPFC neuronal firing rate was reduced and enhanced irregular firing was observed. Moreover, oscillatory activity was altered, both within the mPFC and in coherence of mPFC with the somatosensory cortex (p < 0.05). ConclusionsHearing loss in juvenile rats leads to hyperactive behavior and pronounced play-fighting during development, suggesting a causal relationship between hearing loss and cognitive development. Altered neuronal activities in the mPFC after hearing loss support such effects on neuronal networks outside the central auditory system. This animal model provides evidence of developmental consequences of juvenile hearing loss on prefrontal cortex in absence of language as potential confounding factor.

Evaluation of the diphenyl herbicide, oxyfluorfen, for effects on thyroid hormones in the juvenile rat

Recently, oxyfluorfen, a pre- and post-emergent diphenyl ether herbicide, was identified in our laboratory as an inhibitor of iodide uptake by the sodium iodide symporter (NIS), the first key step in the synthesis of thyroid hormones (THs). This inhibition was observed in vitro, using both a human NIS engineered cell line (hNIS-HEK293T-EPA) and a rat thyroid follicular cell line (FRTL-5). Oxyfluorfen was found to be a potent inhibitor of NIS activity with an EC50 of approximately 2 µM in both cell lines with no observed cytotoxicity at any concentration tested up to 100 μM. The current research tested the hypothesis that oxyfluorfen alters circulating concentrations of THs. This hypothesis was first tested in a pilot study with both juvenile male and female rats exposed to oxyfluorfen for 4 days at 0, 125, 250 and 500 mg/kg/day. Once we identified that this short-term 4-day oxyfluorfen exposure suppressed both total serum thyroxine (T4) and triiodothyronine (T3) at all doses, we tested seven lower concentrations of oxyfluorfen (0.8125 to 62.5 mg/kg day) in an 8-day exposure paradigm to more closely evaluate the dose–response. We found that oxyfluorfen suppressed serum T4 with a LOEL of 3.25 mg/kg/day and T3 with a LOEL 62.5 mg/kg/day. Analytical chemistry of the serum showed an accumulation over time following oral exposure to oxyfluorfen in both the 4- and 8-day groups. Analytical chemistry of the thyroid glands in the 8-day study revealed higher accumulation in the thyroid as compared to the serum (2 to 3- fold at 62.5 mg/kg). No changes in thyroid weight or serum TSH were observed following the 8-day exposure. This study is the first to demonstrate an effect of oxyfluorfen on serum thyroid hormones in the rat. Additional studies are needed to further evaluate the effects on thyroid homeostasis with extended exposures and the potential implications of the observed effects.

Retrieval and savings of contextual fear memories across an extended retention interval in juvenile and adult male and female rats.

Adult rodents exhibit an exceptional ability to retrieve context fear memories across lengthy retention intervals. In contrast, these memories established in younger rodents are susceptible to significant forgetting. The present study aimed to examine the persistence of contextual fear memories established in juvenile and adult Long-Evans male and female rats. Testing 1-day after conditioning, adult males exhibited evidence for greater conditioning than juvenile males, while in females, conditioning did not differ between juvenile and adult rats. In adults, males displayed greater conditioning than females, while in juveniles, males and females reached similar conditioning levels. At the 60-day retention interval, adult sex differences were maintained; however, juvenile rats failed to retrieve this remote contextual fear memory. Next, we examined whether a savings test procedure could recover these remotely established juvenile memories. Following a 60-day retention test, the now adult rats were presented with an additional context-shock pairing to assess the level of savings. While this procedure produced greater conditioning in males than females, the relative savings of this early life memory were similar in males and females. The results of these experiments indicate that adult sex differences in contextual fear memory are maintained across an extended retention interval, while in juveniles, there were no significant sex differences. A novel finding in the present study was that both male and female rats failed to retrieve an initial juvenile memory following an extended retention interval. However, these memories were recovered with a single reminder of the original juvenile experience. (PsycInfo Database Record (c) 2023 APA, all rights reserved).

Effects of different types of neonatal pain on somatosensory and cognitive development in male juvenile rats.

Premature infants are inevitably exposed to painful events, including repetitive procedures, inflammation, or mixed stimulation that may induce long-term behavioral outcomes. Here, we set up three neonatal painful models to investigate their long-term effect on somatosensation and cognition. Three types of neonatal pain models in rat were set up. Rat pups were randomly assigned to four groups. The needling pain (NP) group received repetitive needle pricks on the paws from the day of birth (PD0) to postnatal day 7 (PD7) to mimic the diagnostic and therapeutic procedures. The inflammatory pain (IP) group received the injection of carrageenan into the left hindpaw at PD3 to induce IP in peripheral tissues. The mixed pain group received a combination of the NP and IP (NIP). The control (CON) group was untreated. We performed behavioral and biochemical testing of juvenile rats (PD21-PD26). The NIP group showed a longer hypersensitivity than the NP group, when given a secondary inflammatory stimulation. NP led to insensitivity to anxiety-causing stimuli and impairment of fear memory both aggravated by NIP. NP reduced the expression of synapse-related molecules (GluN1/PSD95/GFAP) in the medial prefrontal cortex, and NIP exacerbated this decrease. The corticosterone secretion in the NIP group increased after the behavioral task, compared with those in other three groups. A combination of NP with inflammation occurring in the neonatal period might aggravate the adverse effects of each on somatosensory and cognitive development of rats, the mechanism of which might be associated with the increase of corticosterone secretion and the dysregulation of synaptic molecules.

The role of thymus graft on the onset of puberty in juvenile male rats

There exists a bidirectional relation between the thymus gland and the hypothalamo- hypophysial-gonadal axis. The thymus secretes various hormones, some of which can regulate the reproductive axis. So, it is worth to explore the possible role of an additional thymus on the onset of puberty in male albino rats. Two groups of male rats aged 5 and 10 days were used for the study. Each subgroup consisted of 4 pups each in control and experimental group. Thymus glands for graft were obtained from newborn male rat pups. Depending on the age group, 5 day or 10-day-old male rat pup were anaesthetized, 2-3 mm incision was made, and a thymus gland was grafted to the axilla. Sham operations were performed to the control pups. Without handling, animals were observed daily for the onset of puberty. On the day of descent of testes, body weight of the animal was noted, blood was collected and used for radio immunoassay. All morphometric measurements were done using an occular micrometer. Volume fraction of seminiferous tubules, intertubular connective tissue of testes, cortex and medulla of the thymus were estimated by point count method. In both the age groups thymus graft advanced the age of descent of testes, and increased body weight and organ weight. It also increased the serum hormone levels. In conclusion, this study indicates that an additional thymus gland has a positive effect on the male reproductive system towards pro-gonadal action, and this effect is more pronounced in older-age groups of rats.

The Goldilocks Principle: Balancing Familiarity and Novelty in the Selection of Play Partners in Groups of Juvenile Male Rats

Like many mammals, rats frequently engage in play fighting as juveniles, an activity that influences the development of socio-cognitive skills. Most studies that assess play are based on staged dyadic encounters, implying that some average quantity and quality of play are sufficient to produce these developmental effects. However, there are individual differences, with some rats not only preferring to play more, but also to have more physical contact than others. Given that rats have individual differences in play, it raises the possibility that rats might express these preferences when playing in groups. To determine whether rats form partner preferences, trials were conducted in which a focal rat was given the opportunity to play with three partners of varying familiarity. One partner was a cage mate, another was housed on the other side of a transparent and perforated divider and so familiar, but not a prior play partner, and the third was a stranger from another cage. A total of 36 focal rats, between 30-36 days of age, were tested and video recorded in 20-minute trials following 2.5 h of social isolation. Focal rats expressed a preference for neighbors over both strangers and cage mates, indicating that balancing between familiarity and novelty influences social play partner preferences. Mechanisms by which this preference might have been established, such as dominance relationships, weight differences, and congruency of play style, were investigated, but none were correlated with the preferences expressed. This group dynamics perspective provides a novel approach to studying play, and more generally, provides insights into social exploration and decision-making.

Repeated mild traumatic brain injury causes sex-specific increases in cell proliferation and inflammation in juvenile rats

Childhood represents a period of significant growth and maturation for the brain, and is also associated with a heightened risk for mild traumatic brain injuries (mTBI). There is also concern that repeated-mTBI (r-mTBI) may have a long-term impact on developmental trajectories. Using an awake closed head injury (ACHI) model, that uses rapid head acceleration to induce a mTBI, we investigated the acute effects of repeated-mTBI (r-mTBI) on neurological function and cellular proliferation in juvenile male and female Long-Evans rats. We found that r-mTBI did not lead to cumulative neurological deficits with the model. R-mTBI animals exhibited an increase in BrdU + (bromodeoxyuridine positive) cells in the dentate gyrus (DG), and that this increase was more robust in male animals. This increase was not sustained, and cell proliferation returning to normal by PID3. A greater increase in BrdU + cells was observed in the dorsal DG in both male and female r-mTBI animals at PID1. Using Ki-67 expression as an endogenous marker of cellular proliferation, a robust proliferative response following r-mTBI was observed in male animals at PID1 that persisted until PID3, and was not constrained to the DG alone. Triple labeling experiments (Iba1+, GFAP+, Brdu+) revealed that a high proportion of these proliferating cells were microglia/macrophages, indicating there was a heightened inflammatory response. Overall, these findings suggest that rapid head acceleration with the ACHI model produces an mTBI, but that the acute neurological deficits do not increase in severity with repeated administration. R-mTBI transiently increases cellular proliferation in the hippocampus, particularly in male animals, and the pattern of cell proliferation suggests that this represents a neuroinflammatory response that is focused around the mid-brain rather than peripheral cortical regions. These results add to growing literature indicating sex differences in proliferative and inflammatory responses between females and males. Targeting proliferation as a therapeutic avenue may help reduce the short term impact of r-mTBI, but there may be sex-specific considerations.

Expression of Angiopoietin-2 in Lung Tissue of Juvenile SD Rats with Lipopolysaccharide-Induced Acute Lung Injury and the Role of Ulinastatin.

This study aimed to observe the expression of angiopoietin-2 (Ang-2) in the lung tissue of juvenile SD rats with lipopolysaccharide (LPS)-induced acute lung injury (ALI) and to clarify the role of ulinastatin (UTI). Ninety 18-21-day-old juvenile SD male rats were randomly divided into five groups (n = 18). ALI rat model was established by intraperitoneal injection of LPS (LPS 10mg/kg), while the control group was given the same dose of normal saline. The UTI intervention group was given the injection of UTI (5000 U/mL) immediately after the injection of LPS, which was divided into UTI low-dose group (LPS + 5ml/kg UTI), UTI medium-dose group (LPS + 10ml/kg UTI), and UTI high-dose group (LPS + 20ml/kg UTI).The respiratory status of each group of rats was observed, and six rats were randomly selected to be killed in each group at 6, 12, and 24h, and the lung tissues were dissected and retained. The pathological changes of the lung tissues were observed by hematoxylin-eosin (HE) staining, the expression levels and locations of Ang-2 and vascular endothelial growth factor (VEGF) in lung tissue were observed by immunohistochemical staining, and the expressions of genes and proteins of Ang-2 and VEGF were detected by quantitative reverse transcription polymerase chain reaction (RT-PCR) and Western blot analysis. Three hours after intraperitoneal injection, rats in the model group developed shortness of breath and the developed respiratory distress progressed over time. The lung pathological changes in the model group were obvious compared with those in the control group, and gradually worsened with time, and the pathological changes of lung in the rats in the UTI intervention group were reduced compared with those in the model group. At different time points, the expressions of Ang-2 and VEGF in the lung tissue of rats in the model group were higher than those in the control group, and were lower in the UTI intervention group than those in the model group. The expressions of Ang-2 and VEGF protein were lower in the low-dose group of UTI group than those in the high-dose group of UTI group at different time points (P < 0.05), and the expressions of Ang-2 and VEGF protein in the low-dose group of UTI were significantly lower than those in the medium-dose group at 12h and 24h (P < 0.05). The expression of Ang-2 was increased in the lung tissue of juvenile SD rats with LPS-induced ALI, and was associated with the degree of lung injury. UTI might attenuate LPS-induced ALI by inhibiting the expression of Ang-2 in lung tissue, and the low dose was more obvious than the medium and high dose.

PM 2.5 juvenile exposure–induced spermatogenesis dysfunction by triggering testes ferroptosis and antioxidative vitamins intervention in adult male rats

PM2.5 derived from automobile exhaust can cause reproductive impairment in adult males, but the toxic effects of PM2.5 exposure on reproductive function in juvenile male rats and its relationship with ferroptosis have not been reported. In this paper, 30-day-old juvenile male Sprague-Dawley (SD) rats were divided into four groups (blank control, vitamin control, PM2.5, and PM2.5+Vitamin). The blank control group was fed normally, and the vitamin control group was given intragastric administration of vitamins in addition to normal feeding. PM2.5 was administered via tracheal intubation. When the rats were treated for 4 weeks until reaching the period of sexual maturity. A mating test was performed first, and then their testicular and epididymal tissues were studied. Compared with control rats, juvenile male rats exposed to PM2.5 showed a decreased sperm count and fertility rate, redox imbalance, damaged mitochondria, a metabolic disorder of intracellular iron ions, and a significant rise in ferroptosis during the period of sexual maturity. After antioxidative vitamins intervention, the redox imbalance, metabolic disorder of intracellular iron ions, and ferroptosis were all alleviated, leading to the following conclusions: after being exposed to PM2.5 from automobile exhaust, male juvenile rats during the period of sexual maturity have significantly decreased reproductive function. The reproductive toxicity of PM2.5 is closely related to oxidative stress and ferroptosis. In addition, ferroptosis decreases and reproductive function is recovered to some degree after antioxidative vitamins intervention.Graphical abstract